In many types of rotating electric machines, static charges, shaft induced currents and extraneous electric currents (collectively referred to herein as “extraneous electric currents”) are generated as a dangerous by-product of the functioning of said rotating electric machine. These extraneous electric currents are especially prevalent in three-phase AC motors controlled by variable frequency speed drives typically utilizing pulse width modulation. These extraneous electric currents typically travel down the shaft of the rotating electric machine and are ultimately discharged into the bearings of the rotating electric machine, which is the path of least resistance. Over time, because of this electrical discharge into the bearings, the bearings become damaged (fluted and pitted) and lose their effectiveness. Initially, this leads to excessive noise, vibration and deficient machine performance. Eventually, it will cause premature, costly, unexpected and dangerous rotating electric machine failure. In fact, bearing failure due to damage from extraneous electric currents is one of the most prevalent causes of rotating electric machine failure. In order to prevent this from occurring, it is necessary to remove the extraneous electric currents from the shaft of the rotating electric machine before the extraneous electric currents reach and damage the bearings and ultimately harm the entire rotating electric machine. It is thus an objective of the present invention to remove these extraneous electric currents from the shafts of rotating electric machines before they damage the bearings and cause premature, unexpected, costly and damaging operational failure.
Prior to the invention of the Constant Force Shaft Grounding Brush Holder (the “CFSGBH”), a number of preventative devices have been utilized in an attempt to eliminate extraneous electric currents from the shaft of a rotating electric machine. The most frequently used has been a fixed circular ring (typically aluminum or metallic) containing carbon strands, filaments or fibers (or any other conductive medium), which protrude from its inner diameter (the “fixed circular ring”). This fixed circular ring is typically mounted on the exterior (sometimes the interior) of the rotating electric machine and surrounds the shaft in such a manner that the carbon strands, filaments or fibers make contact with the shaft as it rotates, with the putative goal of removing the extraneous electric currents from the shaft. This method has proved ineffective because the high resistivity and sub-optimal contact of the carbon strands, filaments and fibers cannot completely remove the extraneous electric currents from the shaft and thus cannot fully protect the bearings and the rotating electric machine from damage. In addition, this method is very costly to install and implement. For example, the cost of the fixed circular ring is typically unreasonably high when compared to the cost of the rotating electric machine to which it is affixed. Further, (i) because of size limitations, the fixed circular ring can generally only be mounted on the exterior of the rotating electric machine; (ii) the rotating electric machine typically has to be uncoupled from its mounting base in order to install the fixed circular ring on the surface of the rotating electric machine; and (iii) a different size fixed circular ring has to be used with each different diameter shaft thereby creating additional costs and limiting flexibility. Moreover, special coatings, tapes, finishes and powders need to be applied to the fixed circular ring and the shaft of the rotating electric machine in order to make the fixed circular ring effective, thereby adding significant costs and contaminants and decreasing the functional efficiency of the rotating electric machine.
It is generally well-know that because of their low resistivity and high conductivity, certain grades of carbon brushes (particularly silver/graphite blends) are more effective than fixed circular rings in removing extraneous electric currents from the shafts of rotating electric machines. However, until the invention of the CFSGBH, carbon brushes have not been optimally nor effectively used to remove extraneous electric currents from the shafts of rotating electric machines. A novel design breakthrough and objective of the present invention from the prior art is its ability to incorporate a true constant force spring in its design in a versatile, standardized, modular, low-profile, cost-efficient, facile manner, which overcomes the limitations of the prior art. There are examples of prior art attempting to utilize a carbon brush to remove extraneous electric currents from the shafts of rotating electric machines. These examples of prior art are generally ineffective because of their design limitations, complexity, cost and predominantly because they did not incorporate a constant force spring to resiliently urge the carbon brush towards the shaft of the rotating electric machine and thus maximize the efficacy of the carbon brush in removing extraneous electric currents from said shaft. Because of this, the carbon brushes depicted in the prior art tended to wear out quickly, did not utilize the optimal spring pressure and vibrated excessively, and thus did not function optimally, failed to effectively remove extraneous electric current from the shaft of the rotating electric machine, reduced their useful brush life and required excessive repair and replacement. The carbon brush and brush holder assembly could not accomplish their intended purpose.